| 摘要 |
PURPOSE:To eliminate the insufficient torque at a heavy load time by always detecting an input current, and always correcting the primary resistance drop of an induction motor due to an increase in a current, thereby preventing the exciting magnetic flux of the motor at the heavy load time. CONSTITUTION:A current detector 10 detects the DC current of a DC bus, compares with the current value from a current value setter 11 at no load time, and detects the increase of the current due to the load. Then, a voltage proportional to the current increase from a correcting voltage output circuit 12 is output, the corrected voltage is added to a voltage output from a voltage frequency ratio circuit 8, and input together with a frequency command from a cushion circuit 7 to a PWM generator 9. Thus, even if a current increases due to a heavy load, the exciting voltage E is held constantly. Thus, the insufficient torque due to the reduction in the exciting magnetic flux can be eliminated at a heavy load time. |
